The present invention relates to cellular radio communication networks allowing communications at various bit rates.
The mechanism of multiple access of mobile stations in such a network is one of the key points in the design of the network.
The present invention relates more particularly to a time division multiple access (TDMA) method.
TDMA systems are used in a number of existing cellular networks, especially those constructed according to the GSM standards designed for essentially fixed communication bit rates. The third-generation mobile radio systems, such as UMTS (Universal Mobile Telecommunication System) will have to support a wide range of services, with bit rates varying from 8 kbit/s to 2 Mbit/s. TDMA systems comparable to those used in GSM have been proposed in order to offer these services and fulfil the objectives of UMTS whilst ensuring some degree of compatibility with the existing GSM infrastructures (see Tero Ojanpera et al, "Comparison of Multiple Access Schemes for UMTS", Proc. of the VTC'97 Conference, Phoenix, May 1997, Vol. 2, pages 490-495).
These proposals generally consider a definition of the radio interface matched to the cellular environment (indoor, outdoor propagation, microcells, macrocells etc.), but not to the type of service to be supported. Thus, for a given cellular environment, it is proposed to use a single bandwidth, the construction of channels with different bit rates resulting only from the allocation of a variable number of elementary timeslots per signal frame. This approach prevents optimization of the spectral resources as a function of the service bit rate, the structure being suitable for one type of bit rate only.
European patent application 0 719 062 discloses a radio communication system in which the used frequency band is divided into "channels", wherein each channel itself may be subdivided into a number of frequency "conduits". In order to allocate radio resource to a certain communication or to a certain service, there is provided either a time splitting of the "conduit" (TDM scheme) or a logic splitting by means of codes (CDMA scheme).
Another time and frequency mapping of the available radio resources is disclosed in European patent application 0 680 168.
A primary object of the present invention is to define a TDMA radio interface structure suitable for supporting a wide range of service bit rates. Another object is that this structure be flexible to use by the operator of the cellular network. It is also desired that this structure be compatible with radio resource optimization mechanisms, such as dynamic channel allocation (DCA) and/or frequency hopping.